python thread scheduler?

[project2501]

to clarifgy, i'm seeing responec times as low as 0.3 seconds when the
client has 5 worker threads... rising to an average of about 8 seconds
with 50 threads... and more ith 100 threads.

here is what the python threads do (simplified):
	while (work units remaining):
		take time
		send request to server
		get responce from server
		take time
		record time difference
		sleep for a small interval (to yield, and to vary the request rate)
		reduce work unit by 1

i get flat graphs of responce time against request rate (which
doubles a specified number of times, after 10 work units. 

i would expect the graphs to start to vary non-linearly ... especially at
higher numbers of threads (say 50 or more) and request rates of 256 per
second or more ...